Qualified astrophysicist Brian May is taking a break from rock music to focus on space rocks. The Queen guitarist has teamed up with researchers from the European Space Agency (ESA) to investigate striking similarities and a puzzling difference between separate bodies explored by space probes. Scientists are analysing the 525 metre diameter Bennu asteroid, which NASA has visited with its OSIRIS-REx spacecraft, and the one kilometre diameter Ryugu, which has been reached by Japan’s Hayabusa2.
Both of the asteroids have a ‘spinning top’ shape and are similar in density.
However, they both contain a distinct difference in water density, leading experts to question if they have a similar origin.
One theory is that as both the asteroids rotate rapidly, centrifugal force could have shaped them in such a middle-heavy way.
My May, who is co-author of the study published in the journal Nature Communications, said: “The shapes of asteroids and their hydration level can serve as real tracers of their origin and history.”
Patrick Michel, CNRS Director of Research of France’s Côte d’Azur Observatory, also lead scientist of ESA’s Hera mission for planetary defence, said: “This spinning top shape of Bennu and Ryugu – including a pronounced equatorial bulge – is shared by many other asteroids, including the primary 780-m Didymos asteroid.
“A leading hypothesis has been that a high rate of spin leads to centrifugal force changing their shape over time, as material flows from the poles to the equator.
“Such a spin can be built up over time by the gradual warming of sunlight – known as the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, named after four different asteroid researchers.
“For Didymos, this might explain where Didymos A’s smaller moonlet came from – forming out of material that broke free of the fast-spinning equator.
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“The most challenging part was simulating the re-accumulation process, which included detailed coding for particle contact including rolling, sliding and shear friction.
“We also looked at the heating level of the post-impact fragments, determining their hydration level.
“What we found was, while the re-accumulation process led to a wide variety of shapes, there is a tendency towards a spinning-top because the aggregating material can be captured in a central disc and eventually forms a spinning top or at least a re-accumulated spheroid.
“This spheroid can then be spun up by the YORP effect to form an equatorial bulge in a rapid timescale in asteroid terms, of less than a million years, explaining what we see on Bennu and Ryugu.”